2.1 Earth's Crust in Motion

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Earthquake: The shaking of plate tectonics
Stress: The force that changes rock and its shape and volume.
Shearing: Stress that pushes rock in opposite directions.
Tension: Stress that pulls on rock making it thinner in the middle.
Compression: Stress that squeezes rock until it folds or breaks.
Deformation: The change in the Earth's crust such as volume or shape is called deformation.
Fault: A break in the Earth's crust where rocks have slipped past each other.
Strike-Slip Fault: The rocks on both sides of the fault move past each other sideways or with up-or-down motion.
Normal Fault: During a normal fault the fault is at an angle where one block of rock lies above the fault and the other block lies beneath the fault.
Hanging Wall: The block of rock that lies above the fault is called the hanging wall.
Footwall: The block of rock that lies beneath the fault is called the footwall.
Reverse Fault: A reverse fault has the same structure as a normal fault but instead of the block going underneath the other, in a reverse fault the blocks of rock move in opposite directions.
Fault-block Mountain: These mountains form when a normal fault uplifts a block of rock.
Folds: Folds are bends in rock that form when compression thickens part of the Earth's crust and shortens it as well.
Anticline: Anticlines form when a fold in rock bends upward forming an arch.
Syncline: Synclines form when a fold in rock bends downward forming a bowl.
Plateau: This area is a large area of flat land that is situated high above sea level.

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Outline

Introduction

• As you are sitting somewhere in your house, suddenly everthing starts to shake and fall.
  • After the shaking ends you turn on the news and you here that an earthquake just struck your area.
    • Earthquakes can be very destructive as they can destroy homes and wreck other things as well.

Stress in the Crust

• For many years people have been wondering what earthquakes are and what causes them.
  • An earthquake is actually the shaking and trembling of plate tectonics and it is caused by stress.
    • There are three types of stresses. They are shearing, tension, and compression.
• Shearing
  • Shearing is the stress force that pushes rock in opposite directions.
    • Shearing can cause rock to break or change its shape
• Tension
  • Tension is the stress force that pulls on rock making it thinner in the middle.
    • Tension is like pulling on a warm piece of gum.
• Compression
  • Compression is the stress force that squeezes rock until it folds or breaks.
    • Compression is like compressing rock like a giant compactor.

Kinds of Faults

• There are three different types of faults.
  • They are strike-slip faults, normal faults, and reverse faults.
• Strike-Slip Faults
  • These faults make rocks on both sides to move past each other sideways or with up-or-down motion.
    • These faults form boundaries between plates ( transform boundaries ) .
• Normal Faults
  • During a normal fault the fault is at an angle where one block of rock lies above the fault and the other block lies beneath the fault.
    • The stress force tension creates normal faults in the places where plates diverge creating a divergent boundary.
• Reverse Faults
  • A reverse fault has the same structure as a normal fault but instead of the block going underneath the other, in a reverse fault the blocks of rock move in opposite directions.
    • Compression creates a reverse fault.

Friction Along Faults

• The movement of rocks along a fault depends on the amount of friction there is between the opposite sides of the fault.
  • A place along the fault where the friction is low, both sides of the fault go by each other without much sticking.
  • A place along the fault where the friction is moderate, the sides of the fault collide together.
  • A place along the fault where the friction is high, the rocks combine together and they stay put.
    • In some of these cases, the stress increases until it is powerful enough to overcome the friction force.

Mountain Building

• There are two ways by which mountains can form.
  • They are by faulting and also by folding.
• Mountains formed by faulting
  • Mountains formed by faulting are called fault-block mountains.
    • These mountains form when a normal fault uplifts a block of rock.
    • An example of fault-block mountain range is the Sierra Nevada of California.
• Mountains formed by folding
  • Mountains formed by folding are actually mountains that have formed when compression thickens part of the Earth's crust and shortens it as well.
    • `An example of mountains formed by folding are the Himalayas in Asia and the Alps in Europe.

Anticlines and Synclines

• Anticlines
  • Anticlines form when a fold in rock bends upward forming an arch.
  • Anticlines are found in many places on the Earth's surface where the stress force compression have folded the surface.
    • One example of an anticline are the Black Hills of South Dakota.
• Synclines
  • Synclines form when a fold in rock bends downward forming a bowl.
  • Synclines are also found in many places on the Earth's surface where the stress force compression have folded the surface.
    • One example of a syncline is the Illinois Basin.

Plateaus

• A plateau is an area is a large area of flat land that is situated high above sea level.
  • It consists of many flat layers, and it is wider than it is tall.
  • One example of a plateau is the " Four Corners " of Arizona, Utah, Colorado, and New Mexico.